1. Field of the Invention
The present invention generally relates to a method and an apparatus for detecting motion vectors. More particularly, the invention relates to a method and an apparatus for detecting motion vectors in which motion vectors are detected with low power consumption.
2. Description of the Related Art
According to the Moving Picture Experts Group (MPEG) of the International Organization for Standardization/International Electrotechnical Commission, Joint Technical Committee 1/Sub Committee 29) (ISO/IEC JTC1/SC29), moving picture data is compressed by detecting a motion vector. In other words, it is necessary to detect a motion vector in order to perform the above type of compression.
FIG. 15 illustrates an example of a known motion vector detecting apparatus. The configuration of this apparatus is disclosed in pages 61 to 68 of the Technical Report of IEICE ICD93-80 (1993-08) as "half-pel-precision motion-vector detecting LSI in compliance with CCIR601".
In this example, search window data (pixel data within a search area) is supplied to a calculating unit 71 from an input circuit (not shown). The pixel data is shifted by columns of a reference block from a side register (SR) 81 to a processing element (PE) 82. Each PE 82 stores pixel data for one search block. Each PE 82 also has predetermined reference block data (template data) for detecting a motion vector. The PE 82 then calculates the difference between the predetermined reference block pixel data and the stored search block pixel data and outputs it to a sum circuit 72. One stage of cascade-connected PEs 82 sequentially transfers each column of pixel data of a search block (reference block) to the subsequent stage of PEs 82 in synchronization with the clock. Similarly, each stage of PEs 82 transfers pixel data. Then, upon inputting a new column of data, the PE 82 again calculates the difference between the reference block pixel data and the search block pixel data and outputs it to the sum circuit 72.
The sum circuit 72 obtains the sum of the absolute values of the differences between the reference block pixel data and the search block pixel data in each search block so as to output the sum to a minimum value detecting circuit 73. The minimum value detecting circuit 73 then detects the position of the search block within the search window obtained when the sum circuit 72 outputs the minimum value.
In this manner, according to the above known type of motion vector detecting apparatus, pixel data is sequentially transferred from one stage of PEs to a subsequent stage of PEs, i.e., pipeline processing is performed to transfer pixel data. Thus, data is overwritten in most of the PEs whenever each row of pixel data is transferred in each clock, causing a current to flow and increasing the power consumption.